Overhead cable

ABSTRACT

An overhead power transmission line formed by stranding at least one outwardly projecting strand at the outermost layer of an overhead power transmission line formed by a plurality of strands. At least the outwardly projecting portion of the outwardly projecting strand is composed of an organic material. The outwardly projecting strand has a projection height H within a range defined as 1.5 mm≦H≦7.0 mm. By setting the projection height H of the outwardly projecting strand equal to or larger than 1.5 mm, the wind noise characteristic can be conspicuously improved. Further, by setting H≦7.0 mm, the outwardly projecting strand comprised by an organic material is made easily crushable, so the gripping portions of spacers, dampers, and other parts which have been conventionally used can be used as they are.

This application is a divisional application filed under 37 CFR §1.53(b)of parent application Ser. No. 08/622,832, filed Mar. 27,1996, now U.S.Pat. No. 6,147,303.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an overhead cable (including anoverhead power transmission line and an overhead ground wire) whichprevents wind noise and corona noise and, at the same time, reduces thewind pressure.

2. Description of the Related Art

When wind blows against a laid overhead power transmission line, forexample, a Karman vortex is generated on the downwind side of theoverhead power transmission line and wind noise is caused. To preventthis wind noise, it is effective to provide a projection at the outerperiphery of the overhead power transmission line to disturb the Karmanvortex.

For this reason, conventionally, for example as shown in JapaneseExamined Patent Publication (Kokoku) No. 53-14146, a spiral rod made ofmetal, formed by an aluminum wire etc., was wound around the outermostlayer of the overhead power transmission line to provide the projectionand this projection was used to disturb the Karman vortex and therebyprevent the wind noise.

When winding a spiral rod made of metal around the outermost layer ofthe overhead power transmission line, however, there arises a problemthat corona noise is apt to be generated during rain.

The cause of this is that the electric field becomes stronger at thesurface of the projection, so when rain is deposited there to form dropsof water which subsequently drop down, a strong discharge occurs.

To prevent the corona discharge described above, it is known to form thespiral rod by a semiconductor material and an insulating material (referto Japanese Unexamined Patent Publication (Kokai) No. 3-277114). Whensuch a spiral rod is used, since the insulating material does not haveany effect on the electric field distribution, the rod is effective forsuppressing corona noise at the time of rain.

However, the work of winding the spiral rod around the outermost layerof the overhead power transmission line was very cumbersome.

Therefore, an overhead power transmission line formed by stranding anoutwardly projecting strand at the outermost layer of the overhead powertransmission line has been proposed (Japanese Examined PatentPublication (Kokoku) No. 6-42328).

When preliminarily winding the outwardly projecting metal strand aroundthe outermost layer of the overhead power transmission line in this way,there is the advantage that it becomes unnecessary to wind a spiral rodlater.

When stranding an outwardly projecting metal strand at the outermostlayer of the overhead power transmission line, however, the weight ofthe overhead power transmission line is increased, and therefore thereis a problem that the strength of the cable supporting structures suchas the steel towers and insulators has to be increased. Further, thereis a problem that it is necessary to newly prepare the gripping portionsof spacers, dampers, and other parts for gripping the overhead powertransmission line to match with the outwardly projecting metal strand.

SUMMARY OF THE INVENTION

The present invention was made in consideration with the above problemsand has its object to provide an overhead cable which reduces the weightof an overhead cable formed by stranding an outwardly projecting strandat the outermost layer of the strands, enables conventional grippingportions of parts to be used as they are, and effectively prevents windnoise and corona noise.

To achieve the above object, the present invention provides an overheadcable formed by stranding at the outermost layer of an overhead cablecomprised of a plurality of strands at least one outwardly projectingstrand, wherein at least the outwardly projecting portion of theoutwardly projecting strand is composed of an organic material.

Preferably a projection height H of the outwardly projecting strand fromthe outer circumferential surface of the ordinary strands positioned onthe outermost circumference is within a range of from 1.5 mm≦H≦7.0 mm.

Preferably a reinforcing core is provided in the internal portion of theoutwardly projecting strand.

Preferably the surface of the outwardly projecting strand is subjectedto hydrophilic processing.

Preferably small uneven portions are provided on the surface of theoutwardly projecting strand.

It is also possible to form the outwardly projecting strand byintegrally forming a semiconductor body formed at a lower portion and aninsulator formed at an upper portion.

It is also possible to strand two outwardly projecting strands adjacentto each other and form a groove between these outwardly projectingstrands.

It is also possible to fit a holding strand in this groove.

Preferably the outwardly projecting strand is provided with ananti-unraveling means for preventing unraveling due to breakage.

Preferably the anti-unraveling means is for example comprised of sideprojections formed on the two sides of the outwardly projecting strand,which side projections are fit in the grooves of the ordinary strandspositioned on the two sides of the outwardly projecting strand.

It is also possible to make the anti-unraveling means bottom projectionsformed at the two sides of the bottom of the outwardly projectingstrand, which bottom projections are pressed inward at the bottoms ofthe ordinary strands positioned at the two sides of the outwardlyprojecting strand.

It is also possible to make the members constituting the bottomprojections semiconductor members separate from the member constitutingthe outwardly projecting strand and join them to the outwardlyprojecting strand.

In the overhead cable according to the present invention, by forming theoutwardly projecting strand by an organic material, the weight of theoverhead cable can be reduced. For this reason, it becomes unnecessaryto increase the strength of the steel towers and other supportingstructures and the cost of construction of the steel towers etc. can bereduced.

Also, by setting the projection height H of the outwardly projectingstrand equal to or larger than 1.5 mm, the wind noise characteristic canbe conspicuously improved. Further, by making H less than or equal to7.0 mm, the outwardly projecting strand made of the organic material canbe easily crushed, so the gripping portions of parts such as spacers anddampers which have been conventionally used can be used as they are.

Further, in the present invention, by providing a reinforcing core inthe internal portion of the outwardly projecting strand, the strength ofthe outwardly projecting strand can be improved, so breakage of theoutwardly projecting strand can be effectively prevented. Further, whena metal is used as the reinforcing core, the linear expansion rate ofthe outwardly projecting strand can be made close to the linearexpansion rate of the ordinary metal strands constituting the cable, soeven when there are severe temperature changes, it is possible tomaintain a state with the outwardly projecting strand reliably strandedin the cable.

Further, by providing an anti-unraveling means for preventing unravelingdue to breakage of the outwardly projecting strand, the outwardlyprojecting strand will not unravel even if breaking, so short-circuitsand other accidents caused due to the unraveling of a broken strand canbe reliably prevented.

Further, when the surface of the outwardly projecting strand issubjected to hydrophilic processing, the water drops will not becomespherical, therefore the corona noise can be effectively prevented.

Furthermore, by providing small uneven portions on the surface of theoutwardly projecting strand, the position of the vortex generated on thedownwind side of the cable can be moved to the rear of the cable, so thedifference of the pressure between the upwind side and downwind sidebecomes small, and therefore the wind pressure can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome more apparent from the following description of the preferredembodiments made with reference to the accompanying drawings, in which:

FIG. 1 is a laterally sectional view of an overhead power transmissionline according to an embodiment of the present invention;

FIGS. 2 to 16 are laterally sectional views of other embodiments of thepresent invention;

FIG. 17 is a laterally sectional view of one part of the overhead powertransmission line according to another embodiment of the presentinvention;

FIGS. 18A to 18D are sectional views of other embodiments of outwardlyprojecting strands useable in the present invention;

FIG. 19 is a partially sectional perspective view of the overhead powertransmission line according to another embodiment of the presentinvention;

FIGS. 20A top 20D are sectional views showing other embodiments ofuneven portions provided on the surface of the outwardly projectingstrand useable in the present invention;

FIG. 21 is a graph examining the change of the wind noise characteristicdue to the change of the projection height of the outwardly projectingstrand according to the embodiment of the present invention;

FIG. 22 is a graph measuring the wind pressure load of an overhead powertransmission line according to an embodiment of the present inventionand overhead power transmission lines according to comparative examples;and

FIG. 23 is a graph examining the effect of reduction of the wind noiseof an overhead power transmission line according to the embodiment ofthe present invention and overhead power transmission lines according tocomparative examples.

FIG. 24 and FIG. 25 are sectional views of the embodiments applying thepresent invention to OPGW.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, the present invention will be explained in detail by referring tothe drawings.

FIG. 1 shows an overhead power transmission line according to anembodiment of the present invention. The overhead power transmissionline of the present embodiment is constituted by stranding two layers ofaluminum strands 2 having a round cross-section on a plurality of steelcores 1 and stranding aluminum strands 3 having an arcuate cross-sectionaround the outer periphery thereof. One of the aluminum strands 3 of theoutermost layer of this overhead power transmission line projectsoutward. This outwardly projecting strand 4 is formed by an organicmaterial.

As the organic material, a plastic, rubber, or the like can be used.Particularly, a nylon, polyethylene, polytetraethylene fluoride, etc.are preferred. The strand 4 formed by the organic material may not onlybe made an insulator, but also a semiconductor or a combination of asemiconductor and an insulator. When the outwardly projecting strand 4is formed by an organic material as described above, the overhead powertransmission line can be reduced in weight.

Further, the projection height H of the outwardly projecting strand 4 ispreferably made 1.5 mm≦H≦7.0 mm. The reason for this will be explainedlater.

Further, the surface of the outwardly projecting strand 4 is preferablyprocessed to make it hydrophilic by a physical means such as sandblasting or a chemical means such as ozone processing, ultravioletirradiation, and acid treatment from the viewpoint of the prevention ofthe corona noise.

FIG. 2 shows the overhead power transmission line according to anotherembodiment of the present invention. A reinforcing core 5 having acircular cross-section is provided in the internal portion of theoutwardly projecting strand 14 formed by the organic material.

As the reinforcing core 5, an iron wire, steel wire, copper wire,aluminum wire, aluminum-coated steel wire, FRP wire, etc. can be used.

By providing the reinforcing core 5 having a circular cross-section inthe internal portion of the outwardly projecting strand 14 formed by theorganic material in this way, the breakage of the outwardly projectingstrand 4 can be effectively prevented. Further, when a metal is used asthe reinforcing core 5, the linear expansion rate of the outwardlyprojecting strand 14 can be made close to the linear expansion rate ofthe aluminum strands 3 constituting the cable, therefore there is anadvantage that even if there are severe temperature changes, it ispossible to maintain a state with the outwardly projecting strand 14stranded in the aluminum strands 3.

FIG. 3 shows an overhead power transmission line according to anotherembodiment of the present invention. A reinforcing core material 6having an arcuate cross-section is provided in the internal portion ofthe outwardly projecting strand 24 formed by the organic material. Whena reinforcing core material 6 having the arcuate cross-section is used,there is an advantage that the strength can be improved over that of areinforcing core 5 having a circular cross-section.

FIG. 4 shows an overhead power transmission line according to anotherembodiment of the present invention. The outwardly projecting strand 34formed by the organic material is obtained by a combination of asemiconductor 34 a formed at a lower portion and an insulator 34 bformed at an upper portion. A reinforcing core 5 having a roundcross-section is arranged inside this. The semiconductor 34 a contactsthe lower portions of the strands 3 at the two sides of the outwardlyprojecting strand 34 and electrically connects the strands 3 of theoutermost layer insulated by the insulator 34 b. For this reason, it ispossible to reliably prevent a gap discharge between the strands 3 ofthe outermost layer positioned on the two sides of the insulator 34.Note that, as the material constituting the semiconductor, one having aconductivity of about 1×10⁻³(%) to 5×10⁻⁵(%) is preferred. Although notparticularly restricted, mention may be made of high molecular polymer,such as polyamide resin, polyetylene resin, polypropylene resin, etc.

FIG. 5 shows an overhead power transmission line according to anotherembodiment of the present invention. Two outwardly projecting strands 44formed by an organic material are arranged in parallel. At the abuttingportions of the two outwardly projecting strands 44, a groove 7 having aU-shaped cross-section is formed. By providing a groove 7 having aU-shaped cross-section at the abutting portions of the two outwardlyprojecting strands 44 in this way, drops of water easy enter into thegroove 7, therefore the drops of water will not form projections, andthe corona noise can be effectively prevented.

FIG. 6 shows an overhead power transmission line according to anotherembodiment of the present invention. The strands 33 of the outermostlayer are constituted by strands having a circular cross-section.Outwardly projecting strands 54 formed by an organic material areprovided at positions facing each other 180 degrees apart.

Note that, in FIG. 2 to FIG. 6, in the same way as the embodiment shownin FIG. 1, the projection height H of the outwardly projecting strands14, 24, 34, 44, and 54 formed by the organic material is defined as 1.5mm≦H≦7.0 mm. Further, in the same way as the embodiment shown in FIG. 1,application of hydrophilic processing to the surface of the outwardlyprojecting strands 14, 24, 34, 44, and 54 is preferred from theviewpoint of the prevention of corona noise.

FIG. 7 to FIG. 11 show an overhead power transmission line according toanother embodiment of the present invention in which an anti-unravelingmeans for preventing unraveling of the outwardly projecting strand 4 isprovided at the overhead power transmission lines of the previousembodiments.

In the embodiment shown in FIG. 7, projections 8 are provided the twosides of the outwardly projecting strand 64 formed by an organicmaterial. Corresponding to these projections 8, recesses 9 are providedin the outermost layer strands 3 positioned at the two sides of thestrand 64. The strands are stranded with each other with the projections8 and recesses 9 fit with each other.

When stranding the outwardly projecting strand 64 and the outermostlayer strands 3 with each other with the projections 8 and recesses 9fit with each other in this way, even if the outwardly projecting strand64 breaks, the strand 64 will not dangle down. Accordingly,short-circuits and other accidents caused when the strand 64 danglesdownward can be reliably prevented.

In the embodiment shown in FIG. 8, projections 10 having the same widthas that of the outermost layer strands 3 are provided at the two sidesof the lower portion of the outwardly projecting strand 74 formed by anorganic material. Each projection 10 is configured so as to be pressedby the outermost layer strands 3 positioned on the two sides. In thisway, by pressing the projections 10 provided at the two sides of thelower portion of the outwardly projecting strand 74 by the outermostlayer strands 3, dangling of the outwardly projecting strand 74 due tobreakage can be effectively prevented. Note that, it is also possible toconfigure the members constituting the projections 10 provided at thelower portion of the strand 74 by a semiconductor member different fromthe strand 74 comprised by the organic material. In this case, in thesame way as the embodiment shown in FIG. 4, it is possible to reliablyprevent a gap discharge between the strands 3 of the outermost layerpositioned at the two sides of the strand 74.

In the embodiment shown in FIG. 9, the outwardly projecting strand 84 isformed by combining a semiconductor 84 a and an insulator 84 b comprisedby an organic material. Projections 11 having a smaller width than thatof the outermost layer strands 3 are formed at the two sides of thelower portion of the semiconductor 84 a. These projections 11 areconfigured so as to be pressed by the outermost layer strands 3positioned at the two sides of the strand 84. By this, the dangling ofthe outwardly projecting strand 84 due to breakage can be reliablyprevented. Further, in the same way as the embodiment shown in FIG. 4,it is possible to reliably prevent a gap discharge between the strands 3of the outermost layer positioned at the two sides of the strand 84.

The embodiment shown in FIG. 10 is a modification of the embodimentshown in FIG. 5. In this embodiment, projections 11 having a smallerwidth than that of the outermost layer strands 3 are provided at the twosides of the lower portions of two outwardly projecting strands 94formed by an organic material. These projections 11 are configured so asto be pressed by the outermost layer strands 3 positioned at the twosides of the strands 94. Further, a holding strand 12 is fit in theU-shaped groove 7 formed between the two outwardly projecting strands94. The holding strand 12 is preferably constituted by a material havinga stronger tensile strength than that of the outwardly projectingstrands 94 and is made by a metal wire such as for example a steel wire.The two ends of this holding strand 12 in the longitudinal direction arefastened by a fastening member etc.

The embodiment shown in FIG. 11 is a modification of the embodimentshown in FIG. 6. In this embodiment, holding strands 12 are provided atthe two sides of the outwardly projecting strands 54 formed by anorganic material. In the same way as the embodiment of FIG. 10, a metalwire such as a steel wire can be used as the holding strands 12 and thetwo ends of the holding strands 12 are fastened by a fastening memberetc.

Note that, in the same way as the embodiment shown in FIG. 1, theprojection height H of the outwardly projecting strands 64, 74, 84, and94 formed by an organic material is defined as 1.5 mm≦H≦7.0 mm and thesurface of the outwardly projecting strand 4 is preferably processed tomake it hydrophilic from the viewpoint of the prevention of coronanoise.

FIG. 12 to FIG. 18 show overhead power transmission lines according toother embodiments of the present invention in which the outwardlyprojecting strands formed by an organic material are provided withanti-unraveling means.

In the embodiment shown in FIG. 12, the lower surface and the two sidesof the outwardly projecting strand 54 formed by an organic material arecovered by a reinforcing material 15 having a U-shaped cross-section,and the outwardly projecting strand 54 is fixed to the reinforcingmaterial 15. As the reinforcing material 15, aluminum plate, aluminumtube, zinc-plated iron plate, composite metal plate, etc. can be used,but the use of the same material as that of the outermost layer strand 3constituting the overhead power transmission line is preferred from theviewpoint of the prevention of galvanic corrosion.

If the outwardly projecting strand 54 formed by an organic material isreinforced by the reinforcing material 15 in this way, even if theoutwardly projecting strand 54 breaks, the strand 54 will not dangledown, so short-circuits and other accidents caused due to the danglingof the strand 54 can be reliably prevented.

In the embodiment shown in FIG. 13, a reinforcing material 115 having apeak-shaped cross-section is affixed to the lower surface of theoutwardly projecting strand 104 formed by an organic material.

In the embodiment shown in FIG. 14, a reinforcing material 15 having aU-shaped cross-section is affixed to the lower surface and two sides ofan outwardly projecting strand 204 formed by an organic materialobtained by combining a semiconductor 204 a and an insulator 204 b.

In the embodiment shown in FIG. 15, reinforcing materials 15 are affixedto the lower surfaces and two sides of two outwardly projecting strands304 formed by an organic material.

In the embodiment shown in FIG. 16, reinforcing materials 15 havingU-shaped cross-sections are affixed so as to cover the lower surfacesand two sides of outwardly projecting strands 54 formed by an organicmaterial arranged at positions facing each other 180 degrees apart.

In the embodiment shown in FIG. 17, a reinforcing material 215 having aU-shaped cross-section is affixed to the lower surface and two sides ofa two-peak type outwardly projecting strand 404 formed by an organicmaterial.

FIGS. 18A to 18D show other embodiments of the outwardly projectingstrands 504, 604, 704, and 804 formed by an organic material andreinforcing materials 515, 615, 715, and 815. In the embodiment shown inFIG. 18A, the outwardly projecting strand 504 formed by an organicmaterial and the reinforcing material 515 having the U-shapedcross-section are integrally formed. In the embodiment shown in FIG.18B, an outwardly projecting strand 604 formed by an organic material isintegrally formed on an reinforcing material 615 having a comb-likeshape. In the embodiment shown in FIG. 18C, a two-peak type outwardlyprojecting strand 704 formed by an organic material and a reinforcingmaterial 715 having a U-shaped cross-section are integrally formed. Inthe embodiment shown in FIG. 18D, a reinforcing material 815 isintegrally formed so as to cover the lower portion of an outwardlyprojecting strand 804 having an I-shaped cross-section.

Note that the shapes of the outwardly projecting strand formed by anorganic material and the reinforcing material are not restricted tothose of the above embodiments.

In the embodiments shown in FIG. 12 to FIG. 18, in the same way as theembodiment shown in FIG. 1, the projection height H of the outwardlyprojecting strand formed by an organic material is defined as 1.5mm≦H≦7.0 mm and the surface of the outwardly projecting strand ispreferably processed to make it hydrophilic from the viewpoint of theprevention of corona noise.

FIG. 19 shows an overhead power transmission line according to anotherembodiment of the present invention. A large number of small unevenportions 17 are formed on the surface of the outwardly projecting strand904 formed by an organic material.

As a means for forming the large number of small uneven portions 17 onthe surface of the outwardly projecting strand 904 formed by an organicmaterial, there are the method of forming uneven portions 17 by pressingby a roll etc. at the time of shaping the strand 904, the method ofdropping a dissolved organic material on the shaped strand 904, themethod of forming uneven portions 17 by pressing by a roll etc. on theshaped strand 904, and so on.

Note that, in FIG. 19, in the same way as the embodiment shown in FIG.1, the projection height H of the outwardly projecting strand 904 formedby an organic material is defined as 1.5 mm≦H≦7.0 mm and the surface ofthe outwardly projecting strand 904 is preferably processed to make ithydrophilic from the viewpoint of the prevention of corona noise.

FIGS. 20A to 20D show various modifications of the small uneven portions17, 117, 217 a, 217 b, 317 a, and 317 b to be formed on the surface ofthe outwardly projecting strand 904 formed by an organic material.

FIG. 20A shows a circular projection 17, while FIG. 20B shows a circularrecess 117. The bottom of the circular recess 117 is not restricted to aflat bottom and may be a curved bottom as well. FIG. 20C shows acombination of ring-like projection 217 a and a circular recess 217 b.The bottom of the circular recess 217 b is not restricted to a flatbottom and may be a curved bottom as well. FIG. 20D shows an examplewherein stripe-like projections 317 a and stripe-like recesses 317 b arealternately formed.

Of course, the shape of the small uneven portions to be formed on thesurface of the outwardly projecting strand 904 formed by an organicmaterial is not restricted to the shapes of the above embodiments.

Next, an explanation will be made of how to make the projection height Hof the outwardly projecting strand formed by an organic material withina range of from 1.5 mm≦H≦7.0 mm.

FIG. 21 is a graph examining the change of the wind noise characteristicdue to the change of the projection height H of the outwardly projectingstrand. This experiment was carried out by blowing wind at a speed of 20m/sec to an overhead power transmission line having a diameter of 32 mm.The black dots show the case of no projection (Comparative Example 1),the x marks show the case of a projection height of 1 mm (Example 1),the black triangles show the case of a projection height of 1.5 mm(Example 2), the black wedges show the case of a projection height of3.0 mm (Example 3), and the black squares show the case of a projectionheight of 7.0 mm (Example 4).

As apparent from the graph, in the case of no projection, the wind noisecharacteristic is conspicuously degraded at 125 Hz. Contrary to this,where the projection height is 1 mm, only a reduction of 9 dB isobtained at 125 Hz, but where the projection height is 1.5 mm or more, areduction of 15 dB or more is obtained. Accordingly, preferably theprojection height is 1.5 mm or more.

On the other hand, even if the projection height is 7.0 mm or more, awind noise characteristic is obtained, but if the projection height is7.0 mm or more, there is a problem that it becomes impossible to use theconventional gripping portions of parts such as spacers and dampers asthey are. For this reason, preferably the projection height is 7.0 mm orless. Namely, where the projection height H is 7.0 mm or more, thecontact between the overhead power transmission line and the grippingportions of the parts is poor. For this reason, stress during vibrationis concentrated at one part of the gripping portions. Accordingly, itbecomes impossible to use the conventional gripping portions of spacers,dampers, and other parts as they are.

FIG. 22 is a view of measuring the wind pressure load per unit length ofthe overhead power transmission lines A, B, and C. The overhead powertransmission line A according to Comparative Example 2 is asteel-reinforced aluminum cable of 810 mm². The overhead powertransmission line B according to Example 5 is the steel-reinforcedaluminum cable of 810 mm² the same as that of Comparative Example 2 butwith an outwardly projecting strand 14 (projection height H=4.0 mm) asshown in FIG. 2. The overhead power transmission line C according toComparative Example 3 is a cable obtained by winding a spiral rod of 6mm² around the outer circumference of a steel-reinforced aluminum cableof 810 mm².

In FIG. 22, the wind speed is set to 40 m/sec, and the wind pressureload of the steel-reinforced aluminum cable of 810 mm² of ComparativeExample 2 is indicated as 100. As apparent from FIG. 22, it is seen thatthe overhead power transmission line according to Example 5 has areduced wind pressure load per unit length compared with ComparativeExample 3. The overhead power transmission line of Comparative Example 2is equivalent to the overhead power transmission line of Example 5 inthe point of the wind pressure load, but inferior to the overhead powertransmission line of the examples in the point of the noisecharacteristic as shown in FIG. 21.

FIG. 23 is a graph examining the wind noise reduction effect of theoverhead power transmission lines I, II, and III. Note that, the windspeed is 20 m/s.

The overhead power transmission line I according to Comparative Example4 is a steel-reinforced aluminum cable of 410 mm². The overhead powertransmission line II according to Example 6 is a steel-reinforcedaluminum cable of 410 mm² the same as that of Comparative Example 4 butwith an outwardly projecting strand 14 (projection height H=4.0 mm) asshown in FIG. 2. The overhead power transmission line III according toComparative Example 5 is a conventional product obtained by winding aspiral rod of 6 mm² around the outer circumference of a steel-reinforcedaluminum cable of 410 mm².

As apparent from FIG. 23, in the overhead power transmission line IIaccording to Example 6, at a frequency of 160 Hz, a wind noise reductioneffect of about 17 dB is obtained compared with the steel-reinforcedaluminum cable I of 410 mm² according to Comparative Example 4.

Further, in the same overhead power transmission lines I, II, and III asthose described above, when the corona noise level at the cable surfacemaximum potential frequency 15 kV/cm was measured, the level was 36.0 inthe line I according to Comparative Example 4, the level was 36.5 in theline II according to Example 6, and the level was 39.0 in the line IIIaccording to Comparative Example 5.

In this way, it is seen that the overhead power transmission lineaccording to the present embodiment has a conspicuously low corona noisecompared with the cable of Comparative Example 5 which is a conventionalproduct.

Note that, the overhead power transmission line according to the presentinvention is not restricted to the above embodiments. The shape of theoutwardly projecting strand formed by an organic material, the number ofstrands, the positions thereof, etc. can be freely selected. Forexample, it is also possible to use three outwardly projecting strandsformed by an organic material and arrange these three strands atpositions 120 degrees apart.

Further, the shape of the strands constituting the overhead powertransmission line is not restricted to a round cross-section or arcuatecross-section. For example a trapezoidal shape, a shape in which theadjoining strands are fit, etc. can be adopted too.

Further, the present invention is not restricted to an overhead powertransmission line according to the above embodiments. It can be appliedalso to an overhead ground wire. As the overhead ground wire, there isan OPGW (optical ground wire) in which a plurality of optical fibers arearranged in the internal portion. By stranding at least one outwardlyprojecting strand with the outermost layer of this OPGW and making atleast the outwardly projecting portion of this outwardly projectingstrand by an organic material, the present invention can be applied alsoto an OPGW.

FIG. 24 shows an overhead cable (OPGW) containing optical fibers whichcomprises an aluminum pack 31 containing optical fibers 30 around whichare stranded eight aluminum-coated steel wires 32 each comprised of asteel core 32A coated by aluminum. A projecting strand 4 is stranded ina groove 35 on the outer circumference.

FIG. 25 shows an overhead cable (OPGW) containing optical fiberscomprised of an aluminum pack 31 containing optical fibers around whichare stranded two kinds of arcuate cross-section segmented strands 33 and34. The strands 33 and 34 have respectively steel cores 33A and 34A. Aprojecting strand 14 is stranded into the place of one outer layerstrand 34 which has been omitted.

The projecting strands in the embodiments explained above may be madethe various forms shown above. They are not limited to one. Severalprojecting strands may be attached at symmetric positions.

Further, when using two projecting strands at symmetric positions, theratio h/D can be made about half that in the case of provision of asingle strand. Further, by making the h/D of the case of the singlestrand 5 to 10 percent, it is possible to reduce the wind noise level by7 to 10 dB compared with the original form of the cable with no suchstrands provided.

What is claimed is:
 1. An overhead cable formed by stranding at leastone outwardly projecting strand at the outermost layer of an overheadcable formed by a plurality of strands, wherein at least an outwardlyprojecting portion of said at least one outwardly projecting strand iscomposed of an organic material, wherein a reinforcing core is providedin an internal portion of said outwardly projecting strand.
 2. Theoverhead cable as set forth in claim 1, wherein small uneven portionsare provided on the surface of said outwardly projecting strand.
 3. Theoverhead cable as set forth in claim 1, wherein said at least oneoutwardly projecting strand is two outwardly projecting strands strandedadjacent to each other and a groove is formed between these outwardlyprojecting strands.
 4. The overhead cable as set forth in claim 3,wherein a holding strand is fit in said groove.
 5. An overhead cableformed by stranding at least one outwardly projecting strand at theoutermost layer of an overhead cable formed by a plurality of strands,wherein at least an outwardly projecting portion of said at least oneoutwardly projecting strand is composed of an organic material, whereinsaid outwardly projecting strand is formed by integrally forming asemiconductor formed at a lower portion and an insulator formed at anupper portion.
 6. An overhead cable formed by stranding at least oneoutwardly projecting strand at the outermost layer of an overhead cableformed by a plurality of strands, wherein at least an outwardlyprojecting portion of said at least one outwardly projecting strand iscomposed of an organic material, wherein said outwardly projectingstrand is provided with an anti-unraveling means preventing unravelingdue to breakage.
 7. The overhead cable as set forth in claim 6, whereinsaid anti-unraveling means is comprised of side projections formed attwo sides of said outwardly projecting strand, and said side projectionsare fit in grooves of the ordinary strands positioned at the two sidesof said outwardly projecting strand.
 8. The overhead cable as set forthin claim 6, wherein said anti-unraveling means are bottom projectionsformed at two sides of the bottom of said outwardly projecting strand,and said bottom projections are pressed inward at the bottoms of theordinary strands positioned at the two sides of said outwardlyprojecting strand.
 9. The overhead cable as set forth in claim 8,wherein members constituting said bottom projections are comprised ofsemiconductor members separate from the member constituting saidoutwardly projecting strand and are joined to the outwardly projectingstrand.